This invention relates to tire repair plates and a of making the same, and more particularly to a tire repair plate molded from a plastic material.
The current practice of repairing a damaged tire and restoring the surface of the repaired area to its original appearance includes a process of machining a metal plate, usually an aluminum plate. Where the plate is used to repair a side wall upon which lettering appears in the tires, the letters must be machined or etched into the surface of the plate which is to fit against the corresponding surface of the tire wall.
The injury in the tire is repaired or mended by filling it with an uncured plug of rubber. The metal side wall or letter plate is placed over the uncured plug in a position corresponding with the original surface and its lettering. The tire and plate are clamped between a pair of heated jaws or curing plates to which heat is applied to a curing temperature of approximately 270-298 deg. F. After the rubber plug is cured, the jaws are removed and the repair plate is removed so that the repaired area is made to look as much like the original tire surface as possible. Various shapes of plates are used for repairing injuries to the side wall or the bead area of the tire. Currently it is not possible to use this method for repairing the tread area of the tire because of difficulty in making corresponding repair plates. when a tire is injured in its tread area, the tire is usually scrapped.
Other methods of repairing tires involving the restoration of the appearance of the surface of the tire, including tread areas, are disclosed in one or more of the following U.S. patents:
______________________________________ 1,338,233 McCormick Apr. 27, 1920 1,349,039 Bitter Aug 10, 1920 1,380,320 Hufford May 31, 1921 2,391,300 Dettling Dec 18, 1945 2,814,830 Leeth Dec. 3, 1957 2,875,470 Goodman Mar. 3, 1959 3,190,338 Wolfe June 22, 1965 ______________________________________
U.S. Pat. No. 2,750,632, issued to Kish, on June 19, 1956 discloses a method of making surface reproduction fixtures, such as a hood model from plastic materials, such as urea and phenol formaldehyde resins.
The following U.S. patents disclose various methods of making reinforced printing plates from plastic material:
______________________________________ 2,075,507 Crowell Mar. 30, 1937 2,272,254 Swan Feb. 10, 1942 4,474,720 Izard Oct. 2, 1984 ______________________________________
The Izard patent discloses a method of casting a liquid resin, such as epoxy in a mold for producing a porous matrix for the wet-end texturing of fiber board at the final suction press roll of a Fourdrinier fiber board machine. After the epoxy resin is poured into the mold, a perforated metal plate is submerged in the liquid resin and ultimately removed from the resin to provide a plurality of studs and channels in the final matrix for conducting water from the processed slurry through a perforated press roll.
The Applicant has himself attempted to make a tire repair letter plate, that is a repair plate to fit over the lettering on the side wall of a tire, by molding various materials, including epoxies, in a mold to accommodate the surface shape of the side wall of the tire. However, these plates were not satisfactory because they would not transfer the curing heat to the repair area of the tire fast enough. At the suggestion of REN plastics company, the producers of the casting resin which Applicant attempted to mold tire repair plates, Applicant attempted to improve the thermal conductivity of the epoxy plates by the introduction of aluminum filings mixed with the epoxy. Experimental tire repair plates made with the mixture of epoxy and aluminum filings also did not transfer the heat to the repair area with sufficient speed. The Applicant also experimented with a mixture of aluminum chips and epoxy, but the resultant tire repair plates were no more successful than were the plates including a mixture of epoxy and aluminum filings.
The Applicant introduced other materials into the epoxy in order to improve the heat transfer characteristics of the finished repair plate. In one experiment, the Applicant impressed a steel wire screen, that is, chicken wire, into the liquid epoxy to improve the heat conductivity, but the finished plate would not transfer the heat fast enough to cure the raw rubber repair material in a tire. Applicant then used aluminum rods wrapped in spaced parallel relationship with aluminum wires in the epoxy material. However, the resulting repair plates were not satisfactory from a heat transfer standpoint. He tried other types of aluminum arrangements without success.
Applicant then impressed a perforated steel plate as a backing material in the liquid epoxy permitting it to float through the holes in the plate. After the plate was completed, he conducted temperature tests, which resulted in an improved heat transfer capability. Then he used an aluminum perforated plate as a backing material immersed in the resin, since aluminum has a higher heat conductivity than does steel. The heat transfer capabilities of the completed epoxy late with the perforated aluminum plate improved. He also experimented with different brands of casting epoxies and bound that they produced about similar results.
By cutting open one of the epoxy plates which had failed he heat transfer tests, he discovered that there were air voids in the epoxy plate. By experimenting with different and longer curing periods, he discovered that the heat conductivity of the finished repair plate was improved.
Applicant has also experimented with other materials for molding a tire repair plate, such as Babbit metal, Plaster of Paris, and concrete, and found that all of these failed. Not only must the finished plate be capable of a minimum heat conductivity, but must also have dimensional stability and minimum tensile and compressive strengths. He found that Babbit metal distorts excessively, since it has an expansion of approximately 0.015-0.050 inches per inch, whereas casting epoxy resins have an expansion factor of only 0.003-0.004 inches per inch. Moreover, the heated epoxy resins will not expand more than 0.005 inches per inch. Furthermore, it was difficult to extract the Babbit metal from the mold because of an inadequate release agent.
Many plastic materials could not be used because they would not Withstand the curing temperatures of rubber, in the order of 270-298 deg. F.
Applicant also found that Babbit metal had inadequate tensile strength, as does Plaster of Paris and concrete. In the repair of tires, the heated jaws or clamps which are used to squeeze the tire repair area are subjected to 45-55 psi pressure for the repair of passenger vehicle tires, and 95-100 psi for the repair of truck tires.
Applicant has also successfully used perforated copper backing plates within the casting epoxy resin for producing successful tire repair plates, but has found that the copper is too expensive.